Encephalitis-associated antibodies: retrospective analysis of 5 years data from the NHNN neuroimmunology laboratory

<h3>Background</h3> Rarer antibodies associated with encephalitis are increasingly requested through specialist laboratories but little is known about the clinical utility and cost effectiveness of these requests. <h3>Methods</h3> We audited National Hospital of Neurology and Neurosurgery (NHNN) Neuroimmunology laboratory data for serum encephalitis-associated antibody requests. All requests for DPPX, IgLon5, Neurexin-3-alpha, GABA-A R and GABA-B R antibodies between 01/01/18 and 27/07/23 were identified. <h3>Results</h3> Of a total 1655 test requests, 24 (1.45%) were positive, identifying 10 separate individuals with antibody-associated encephalitis (3 DPPX, 4 IgLon5 and 3 GABA-B R). DPPX requests were most likely to be positive (1.83%), followed by IgLon5 (1.78%), then GABA-B R (0.78%). There were no positive results for Neurexin-3-alpha or GABA-A R. <h3>Cost Analysis</h3> The per patient ‘hit rate’ was 0.6%. Cost of tests ordered was £94395 to identify 10 patients from 1655 attempts. The cost per positive ‘patient’ was £9440. <h3>Conclusion</h3> Autoimmune encephalitis-associated antibodies are a common request at the NHNN Neuroimmunology laboratory. The cost of tests over the last 5 years has been nearly £100000 to identify 10 patients with these conditions. More focussed, targeted and phenotype- supported requesting as well as further development of screening assays could reduce NHS cost substantially.